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Lab 3 ADC
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Diff: main.cpp
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/main.cpp Tue Jan 31 23:02:02 2017 +0000 @@ -0,0 +1,78 @@ + +// LAB 3 SAMPLE PROGRAM 1 + +#include "mbed.h" +#include "rtos.h" + +Ticker tick; // Ticker for reading analog +AnalogIn ain(A0) ; // Analog input +DigitalOut led1(LED_RED); // Red LED + +Serial pc(USBTX, USBRX); // tx, rx, for debugging + +// Message type +typedef struct { + uint16_t analog; /* Analog input value */ +} message_t; + +// Mail box +Mail<message_t, 2> mailbox; + +// Function called every 10ms to read ADC +// Low pass filter +// Every 10th value is sent to mailbox +volatile int samples = 0 ; +volatile uint16_t smoothed = 0 ; +void readA0() { + smoothed = (smoothed >> 1) + (ain.read_u16() >> 1) ; + samples++ ; + if (samples == 10) { + // send to thread + message_t *mess = mailbox.alloc() ; // may fail but does not block + if (mess) { + mess->analog = smoothed ; + mailbox.put(mess); // fails but does not block if full + } + samples = 0; + } +} + +// Write voltage digits +// v Voltage as scale int, e.g. 3.30 is 330 +void vToString(int v, char* s) { + s[3] = '0' + (v % 10) ; + v = v / 10 ; + s[2] = '0' + (v % 10) ; + v = v / 10 ; + s[0] = '0' + (v % 10) ; +} + +// Main program +// Initialise variables +// Attach ISR for ticker +// Procss messages from mailbox +int main() { + led1 = 1 ; // turn off + int volts = 0 ; + const int threshold = 100 ; + int counter = 0 ; + char vstring[] = "X.XX\r\n" ; + + tick.attach_us(callback(&readA0), 10000); // ticks every 10ms + while (true) { + osEvent evt = mailbox.get(); // wait for mail + if (evt.status == osEventMail) { + message_t* mess = (message_t*)evt.value.p ; + volts = (mess->analog * 330) / 0xffff ; + mailbox.free(mess) ; // free the message space + if (volts > threshold) led1 = 0 ; else led1 = 1 ; + vToString(volts, vstring) ; + counter++ ; + if (counter == 10) { // limit bandwidth of serial + pc.printf(vstring) ; + counter = 0 ; + } + } + + } +}